Hidroquímica e qualidade das águas subterrâneas do Sistema Aquífero Dunas-Barreiras na região de Parnamirim, RN

Abstract

The study area is inserted in the hydrographic basin of Pirangi river, located in the west coast of Rio Grande do Norte state, covering 370 km² in the Parnamirim region. The area presents a high hydrogeological potential, whose water resources has been widely exploited over the years. The main objective of this dissertation, considering the importance and increasing use of this resource, is characterize the groundwater quality and diagnose hydrochemical changes due the urban development and agriculture in the region. In this sense, it was initially made an assessment of use and land occupation in the whole area, identifying existing activities and the might influence water contamination. Based on these characteristics, the study area was divided in three subareas, to compare the hydrochemical situation between them. For the hydrogeochemical recognition in the defined monitoring network, it was performed field work to collect samples for chemical analysis, in order to interpret the situation of the Dunas-Barreiras Aquifer System. Therewith, many measurements were obtained such as electrical conductivity, total dissolved solids, major cations (sodium, calcium and magnesium), major anions (chloride, sulfate and bicarbonate), iron, potassium, carbonate, nitrate, ammonia, boron, pH, and total hardness; the analysis results were interpreted using statistical methods, hydrochemical maps and Piper and Expanded Durov diagrams; and a study of groundwater quality was conducted for certain uses. The hydrochemical facies that prevails in the study area is sodium chlorinated. The results indicate that the groundwater have generally good quality with low salinity. However, there is a tendency to contamination originating from the northern part of the area, closer to the center of Parnamirim city, which has been undergoing urban expansion processes in the last years. The same tendency is seen in the portions which are agricultural crops and livestock, in the western area. The east portion of the area, subarea which comprises ponds and dunes systems, is the one with lower salinity levels and, therefore, more preserved quality. These findings indicate that the direction in the decreasing of water salinity (towards east) follows the direction of the groundwater flow.